Balloon Cones and Waists Thinning Methodology

ABSTRACT

Medical balloons and balloon preforms are made by methods which include the step of selectively removing material from the proximal and/or distal ends of a segment. In the case of a thermoplastic material characterized by one or more glass transition temperatures, the segment may optionally be maintained at a temperature below the glass transition temperature of the segment during the material removal step.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No. 09/401,618filed Sep. 22, 1999 which is a Continuation-in-part of application Ser.No. 09/076252 filed May 11, 1998, and issued as U.S. Pat. No. 6,024,752,the contents of both of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a method for making balloons forcatheters used in medical dilatation procedures.

Balloon catheters are being used extensively in procedures related tothe treatment of blood vessels. For example, arterial stenosis iscommonly treated by angioplasty procedures which involve insertingballoon catheters into specific arteries. Balloon catheters have alsobeen found useful in procedures involving dilation of body cavities.

The most widely used form of angioplasty makes use of a dilatationcatheter which has an inflatable balloon at its distal end. Usingfluoroscopy, a physician guides the catheter through the vascular systemuntil the balloon is positioned across the stenoses. The balloon is theninflated by supplying liquid under pressure through an inflation lumento the balloon. The inflation of the balloon causes stretching of ablood vessel and pressing of the lesion into the blood vessel wall toreestablish acceptable blood flow through the blood vessel.

In order to treat very tight stenoses with small openings, there hasbeen a continuing effort to reduce the profile of the catheter so thatthe catheter can reach and pass through the small opening of thestenoses. There has also been an effort to reduce the profile of thecatheter after an initial use and deflation of the balloon to permitpassage of the catheter through additional lesions that are to betreated or to allow entry and retreatment of lesions that reclose afterinitial treatment.

One factor manipulated to reduce the profile of the dilatation catheteris the wall thickness of the balloon material. Balloons for dilatationballoon catheters have been made from a wide variety of polymericmaterials. Typically the balloon wall thicknesses have been on the orderof 0.0003 to 0.003 inches for most materials. There have been continuingefforts, however, to develop ever thinner walled balloon materials,while still retaining the necessary distensibility and burst pressurerating, so as to permit lower deflated profiles.

The profile of the deflated balloon is limited by the thickness of thewaist and cone portions of the balloon. Usually, the waist and cone wallthicknesses are thicker than that of the body of the balloon due to thesmaller diameter of the waist and cone portions. In order to reduce theoverall profile of the deflated balloon, reduction of the wall thicknessof the waist and cone portions must be addressed.

Prior art balloon forming techniques involve stretching and blowing ofthe balloon from a segment of extruded polymer tubing. Balloons producedby stretching and blowing a tubular preform or “parison” typically havemuch thicker waist and cone walls than the wall thickness of their bodyportions. The thicker cone walls contribute to the overall thickness ofthe catheter, making tracking, crossing and recrossing of lesions moredifficult. Further, thick cones interfere with refolding of the balloonon deflation so that the deflated balloon can only be further insertedor withdrawn with difficulty, occasionally even damaging the bloodvessel. Thin wall thicknesses enable the deflated balloon to remainnarrow, making it easier to advance the balloon through the arterialsystem.

There have been several solutions proposed for reducing the cone orwaist thickness of catheter balloons in U.S. Pat. No. 4,906,241, U.S.Pat. No. 4,963,37, U.S. Pat. No. 5,087,394, U.S. Pat. No. 5,304,340, EP318,919 and EP 485,903. U.S. Pat. No. 4,906,241 and U.S. Pat. No.4,963,37, both to Noddin, disclose heating a portion of the balloonpreform to a desired temperature and drawing the segment so as to form anecked down region while maintaining a portion of the preform in acrystalline state. The preform may then be blown into a balloon. U.S.Pat. No. 5,304,340 to Downey discloses a method of making a dilatationballoon employing a reverse temperature gradient across the sidewall ofa parison and drawing and expanding the parison subject to thetemperature gradient.

EP 318,919 to Noddin et al. discloses a procedure in which a portion ofthe tube is crystallized to render it dimensionally stable under heatedconditions. The portion stabilized cannot be appreciably inflated ordrawn. The tube is heated in a heated bath and as one end is secured inplace the other is drawn to a desired length and in the process isnecked-down. The tube is drawn down to a constant diameter sleeve. Afterthe initial necking-down of the tube, the tube is reversed in the bathand the second necked-down portion is formed by the same procedure.After the preform is complete the tube is submerged horizontally andrestrained at both ends. Two conical portions at opposing ends arearranged to define the shape of the tapered sections of the balloon.Simultaneously the tube is drawn and expanded without constraint untilthe molecules of the wall material in the balloon region becomestabilized in a biaxially oriented condition. The portions of the tubehaving the preform tapers expand until they are constrained to the shapeof the constraining cones.

U.S. Pat. No. 5,087,394 discloses a method of forming a balloon whereina length of polymer tubing is formed by drawing the tubing material froman extruder using an extruder die and then irradiated. The methodinvolves positioning an internal support mandrel within the tubing andcompressing a portion of the intermediate segment onto the mandrel witha body clamp. The end segment is heated and stretched longitudinally tothe desired length. The process of pulling the tube through a restrictedhot die or body clamp forms the necked portions and thin waist segments.The other end segment is optionally stretched in a similar manner. Thetubing is then heated, and radially stretched by blow-molding to definethe balloon and cooled.

EP 485,903 describes a method wherein a tubular parison is formed of adrawable or orientable polymer. It is heated in a metal mold in therange from the second-order transition temperature to the first-ordertransition temperature of the polymer used. The parison is stretched inthe direction of its axis and then inflated radially resulting in abiaxially-drawn or biaxially oriented crude balloon. The parison is thencooled below the second-order transition temperature and deflated. Thetapered portions of the crude balloon are redrawn by stretching toreduce their wall thicknesses. The balloon is inflated again and heatedabove the second transition temperature and then cooled.

The Levy patents (US Re 32,983 and Re 33,561) teach drawing the tubingby axially pulling the tube in a uniform manner apart and then expandingthe tube with fluid in a confining apparatus. The stretch process occursat a temperature above the glass transition temperature and below themelting temperature of the tubing material.

Another method of reducing the cone thickness of balloons is disclosedin U.S. Pat. No. 5,826,588 to Forman, the contents of which areincorporated herein in their entirety by reference. An excimer laser isused to remove portions of the cones from a balloon via photochemicalablation. This materials removal process occurs after the balloon hasbeen formed.

It is possible to make balloons from a variety of materials that aregenerally of the thermoplastic polymeric type. Such materials mayinclude: polyethylenes, ionomers, ethylene-butylene-styrene blockcopolymers blended with low molecular weight polystyrene and,optionally, polypropylene, and similar compositions substitutingbutadiene or isoprene in place of the ethylene and butylene; poly(vinylchloride); polyurethanes; copolyesters; thermoplastic rubbers;silicone-polycarbonate copolymers; polyamides; and ethylene-vinylacetate copolymers. Orientable polyesters, especially polyethyleneterephthalate (PET), are among the preferred materials for formingcatheter balloons.

Other references illustrating the materials and methods of makingcatheter balloons include: U.S. Pat. No. 4,47,989 and U.S. Pat. No.4,456,000 to Schjeldahl et al, U.S. Pat. No. 4,490,421, US Re 32,983 andRe 33,561 to Levy, and U.S. Pat. No. 4,906,244, U.S. Pat. No. 5,108,415,U.S. Pat. No. 5,156,612 to Pinchuck et al. and U.S. Pat. No. 5,807,520to Wang et al.

All US patents and applications and all other published documentsmentioned anywhere in this application are incorporated herein byreference in their entirety.

SUMMARY OF THE INVENTION

There remains a need to continue to improve balloon wall strengths whilesimultaneously reducing their wall thickness. The present inventionaddresses these needs by reducing the wall thickness of cone and waistportions. The resulting balloon is smaller in size for easier insertioninto the body lumen.

The present invention in one aspect is directed to a method comprisingthe steps of providing a segment of thermoplastic material having apredetermined wall thickness and length, removing material from aportion of at least one of the distal and proximal ends of the segmentto achieve a desired reduced thickness while maintaining the temperatureof substantially all of the segment below the glass transitiontemperature of the thermoplastic material or below the highest glasstransition temperature if the material is a block copolymer so as toform a balloon preform.

The method may additionally comprise the step of drawing the preform toa predetermined length. Desirably, during the drawing step, the wallthickness of the center portion does not substantially change and theproximal and distal ends form a first cone and waist and a second coneand waist, respectively. Also desirably during the drawing, thetemperature of the segment is maintained below the glass transitiontemperature of the thermoplastic material or below the highest glasstransition temperature if the material is a block copolymer so as toform a balloon preform.

The method may additionally comprise the step of expanding the balloonpreform in a mold to produce a balloon, the balloon having a bodyportion, wherein the center portion of the segment becomes the balloonbody portion.

In accordance with the inventive method, the removing step may beaccomplished via a variety of techniques including grinding and etching.

The invention is also directed to balloon preforms and balloons made inaccordance with the inventive methods.

The invention is also directed to a medical balloon having a proximalwaist portion, a proximal cone portion, a body portion, a distal coneportion and a distal waist portion wherein at least one of the proximalcone and waist wall thicknesses and distal cone and waist wallthicknesses is less than the body wall thickness, at least one of theproximal waist and cone portions and distal waist and cone portionshaving had material removed therefrom.

The invention is also directed to a medical balloon having a distal conewith a wall thickness of the distal cone which is less than the wallthickness of the proximal cone.

The invention is also directed to a medical balloon which when inflatedhas a constant wall thickness over substantially the entire length ofthe balloon.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a perspective view of an angioplasty catheter having anexample of a balloon fabricated from the inventive method mountedthereon.

FIGS. 2 a, 2 b, 2 c and 2 d illustrate the results of various processsteps in forming a catheter balloon, depicting respectively, sideelevational views of a tube of polymer material used to form theballoon, the tube of FIG. 2 a with material removed therefrom, astretched polymer tubing preform prepared from the tube, and a formedballoon prepared from the stretched polymer tubing preform.

FIG. 3 is a schematic view of a centerless grinding device that may beuseful in the practice of the method of the invention.

FIG. 4 is a schematic view of a benchtop grinder and die for use ingrinding the balloon preform or balloon.

FIG. 5 a is a schematic of a portion of a balloon with a grindtransition half way along the cone.

FIG. 5 b is a schematic of a portion of a balloon with a grindtransition at the body-cone interface.

FIG. 6 a is a schematic of a portion of a balloon with a grindtransition two thirds of the way along the cone.

FIG. 6 b is a schematic of a portion of a balloon with a grindtransition at the body-cone interface.

FIG. 7 is a schematic of a portion of a balloon with a grind transitiontwo thirds of the way along the cone.

FIG. 8 is a schematic of a portion of an inventive balloon.

FIG. 9 shows the relationship between load and extension for a controlballoon and several inventive balloons.

DETAILED DESCRIPTION OF THE INVENTION

While this invention may be embodied in many different forms, there aredescribed in detail herein specific preferred embodiments of theinvention. This description is an exemplification of the principles ofthe invention and is not intended to limit the invention to theparticular embodiments illustrated.

The dilatation balloon fabricated by the present inventive method isillustrated generally at 100 in FIG. 1, mounted at the distal end of anelongated catheter 110. Catheter 110 is conventional in itsconstruction, providing a lumen communicating with the interior ofinflatable balloon, for inflation and deflation of the balloon, andother optional features conventional in the dilatation catheter art. Theballoon 140 is in its inflated configuration. The balloon 140 is formedof a thermoplastic polymer material which provides the balloon with itsessential compliance characteristics. It may be any thermoplasticpolymer suitable for use as an angioplasty balloon material. Preferredmaterials include thermoplastic elastomers, suitably, polyamideelastomers, such as Pebax® 4033, 5533, 6333, 7033 or 7233polyester/polyether elastomers such as Arnitel EM 740 (DSM Engineering),and polyurethane elastomers such as Pellethane 2102-80D. Otherthermoplastic materials such as PET (polyethylene terephthalate), PBT(polybutylene terephthalate), Surlyn® (polyethylene ionomer), nylon,ethylene-vinyl acetate and others elsewhere described as useful forpreparing balloons may be employed. Additional non-thermoplasticmaterials from which the balloon may be made include latex and PTFE.

As shown in FIG. 1, the balloon has several different regions includingregion B-C which comprises the proximal waist portion 112, region C-Dwhich comprises the proximal cone portion 113, region D-E whichcomprises the body portion 114, region E-F which comprises the distalcone portion 115 and region F-G which comprises the distal waist portion116.

The method of the invention is performed by providing a segment oftubing 120, as shown in FIG. 2 a, of a suitable balloon material.Desirably, the tubing is extruded. Any conventional extruder may beemployed to extrude the tubing. While the tubing is desirablycylindrical, other shaped tubing may be used as well.

At least the center portion 120 b of the polymer tubing 120, whicheventually becomes the balloon, is maintained at a temperature belowabout the glass transition temperature of the tubing as described inmore detail below. At this point the polymer tubing has three sections,a proximal end 120 a, a distal end 120 c and a center portion 120 b.

Polymer material from at least one of the proximal and distal endportions of the tubing 120 is removed to a desired thickness preferablywhile maintaining the temperature of at least a portion of the segmentbelow about the glass transition temperature (Tg) of the thermoplasticmaterial (or below about the highest glass transition temperature if thematerial is a block copolymer). Temperatures as high as 25° C. above Tgare contemplated. Desirably, the temperature will be maintained at Tg orbelow. As shown in FIG. 2 b, material has been removed from both theproximal 120 a and distal 120 c end portions of the tubing 120.Desirably, the entire segment will be maintained below the glasstransition temperature. Super-cooling the tube further below Tg, at thepoint where material is removed, may yield higher quality materialsremoval. Of course, where the glass transition temperature of thematerial is above room temperature, the material removal can be carriedout at room temperature with no cooling or minimal cooling of thematerial.

The invention also contemplates removing material from the tubing at atemperature exceeding the glass transition temperature of the material.In the case of balloon materials which are not characterized by one ormore glass transition temperatures, the invention in one aspectcontemplates maintaining the material at a temperature below ambient andin another aspect contemplates materials removal at ambient temperature.

In one embodiment, material is removed from both the proximal and distalends of the polymer tubing to a desired thickness. The amount ofmaterial removed from both ends may be the same or different.

The material may be removed from the proximal and/or distal end portionsof the segment by grinding. While any suitable grinding process may beemployed, the segment desirably will be subject to a centerless grind. Aschematic of a centerless grinder is shown in FIG. 3. Typically, asegment 120, supported on rest blade 122, is fed at one end into acenterless grinder, shown generally at 150, and guided between twogrinding wheels (work wheel 154 and regulating wheel 158) that rotate inthe same direction at different speeds. Segment 120 rotates as a resultof its contact with regulating wheel 158 and is ground to a specifieddiameter or wall thickness dictated by the distance between the faces154 a and 158 a of the two grinding wheels. One of the grinding wheels,typically the regulating wheel, may be moved so as to vary the distancebetween the faces of the grinding wheels during the grinding process.The segment advances through the grinding machine as a result of itscontact with the grinding wheels. Specifically, one of the grindingwheels, typically the regulating wheel, rotates along an axis that isalmost parallel to the axis of rotation of the segment being ground, butslightly skewed in a vertical plane, so that its contact with thesegment causes the segment to move forward through the machine. Asuitable centerless grinder which may be used is the Royal MasterGrinder model number TG12X3.

As the segment moves forward through the grinder, the grinding actionmay be stopped and restarted at a later time thereby allowing for theproximal and distal ends to be ground without grinding the body portionof the segment.

A number of factors affect the rate at which the segment moves throughthe grinding machine and the rate at which wheels must be changed.Temperature, regulating wheel rotation rate (in revolutions perminute—rpm), regulating wheel tilt angle, slippage, type of coolantused, grinding wheel material, segment diameter, segment material, andsegment uniformity may affect the feed rate. As may be appreciated fromthe description of the centerless grinding process, having a straightand preferably uniform tubing segment is essential to effectivecenterless grinding.

Where the materials removal is accomplished by grinding with a benchtopgrinder, the tubing segment 120 may be supported by a die of suitablelength such as that shown in FIG. 4, that is fixed to the grindingmachine. Desirably, the die, shown generally at 162, will be tubularwith half of the die cut away in the middle third 166 of the die toprovide access to the segment. The first 170 and second ends 174 of thedie have a bore therethrough to allow the segment 120 to be heldtherein. Also desirably, there will be a minimal clearance between theouter diameter (OD) of the segment and the inner diameter (ID) of thedie. A mandrel may also be used in place of or in addition to the diefor support as needed.

Material is removed from segment 120 by applying rapidly rotatinggrinding wheel 178 to the segment. The grinding wheel is rotated at asuitable rate which will depend, inter alia, on the type of material,the amount of material to be removed, the type of grit on the grindingwheel and the availability of coolants. Rates of about 2000 revolutionsper minute or higher have been found to be suitable. Tubing segment 120is rotated within die 162 during the grinding process to ensure uniformmaterial removal.

The segment may also be ground using other suitable devices such as abelt sander.

Desirably, as the segment is ground, a coolant is applied to the segmentto prevent heating of the segment. A coolant such as water or saline maybe misted onto the segment. Other suitable coolants including air andother gasses such as carbon dioxide, nitrogen, argon andchlorofluorocarbons may also be used. Additional, cryosprays as areknown in the art may be used as well. Of course, if the glass transitiontemperature of the material is above room temperature, the grinding maybe carried out at room temperature with no or minimal additional coolingof the segment.

Heating of the segment as a result of the material removal may also becontrolled by altering the material removal rate. By slowing the rate ofmaterial removal such as by grinding, heat buildup in the segment may bereduced.

The grinding wheel used to grind the segment desirably employs a finegrit. A 120 mesh silicon carbide grit has proven suitable for use withPebax®, PBT and PET balloons and balloon preforms although other sizeand type grits including diamond, silica and aluminum may also besuitable for PET and other balloon materials. With the use of such agrit, the resulting ground surface will be smooth thereby avoiding acratered or otherwise irregular surface.

Other suitable techniques for removing material may also be employedsuch as chemical etching. In the case of chemical etching, a mask isapplied to the segment except in the regions from which material is tobe removed. Polymer etchant is then applied to the exposed portions ofthe segment so as to etch away a desired amount of tube material. Thesegment is then rinsed off and the mask removed.

The selective masking of the segment may be accomplished by a variety ofsuitable techniques as are known in the art.

Where material is removed from the waist portion, the desired thicknessof the balloon waist portion will depend on how the balloon is affixedto the catheter. Where the balloon is adhesively bonded to the catheter,the thickness after the materials removal must be such that the waistsection of the balloon will still have sufficient strength. Where theballoon is heat bonded to the catheter, the balloon may have a thinnerwaist without the strength limitations of adhesive bonds.

In either case, both distal and proximal ends will desirably be as thinas possible while still maintaining sufficient bond strength with thecatheter shaft. A waist thickness of approximately 0.001″ plus or minus0.0004″ is particularly desirable.

Because the distal waist portion of a balloon blow molds to a diameterless than the proximal waist portion, typically, in the absence ofmaterial removal the distal waist portion of the balloon will be thickerthan the proximal waist portion. This difference in diameters should betaken into account in determining how much material should be removedfrom the various portions of the segment.

In a preferred embodiment, sufficient material is removed from thedistal waist so that the distal waist is thinner than the proximal waistin order to achieve increased flexibility. Additionally, the proximalwaist need not be as thin as the distal due to how the waist mates upwith the rest of the catheter shaft.

The tube may then be formed into a balloon using known balloon formingtechniques. One such suitable technique is disclosed in U.S. Pat. No.5,807,520 to Wang et al.

Another suitable technique for forming the balloon involvesprestretching the tube and expanding the tube into the form of a balloonby blow molding.

The segment of polymer tubing is optionally prestretched on either sideof the center portion 120 b by elongating proximal 120 a and distal 120c ends axially. Referring to FIGS. 2 a-2 d, the prestretching processcomprises applying an axial stretching force to the polymer tubing 120,allowing the polymer tubing to stretch while maintaining the axialstretching force and finally allowing the stretched polymer tubing 70 toreach approximately room temperature. In so doing, the proximal anddistal ends form a first and second waist, respectively.

Once the prestretch is complete, the stretched polymer tubing 70 isradially expanded into the form of a balloon 140 by using a moldingprocess. The molding process comprises placing the stretched polymertubing 70 in a mold, heating the mold and expanding the stretchedpolymer tubing radially by means of internal pressure. After sufficienttime has passed for the balloon to form, the mold is cooled and theballoon 140 is removed.

The invention is also directed to the formation of a balloon bystretching a preform and subsequently removing material from theproximal and/or distal waist and/or cone portions of the balloonpreform. The materials removal may also occur prior to or followingblowing of the balloon and in one aspect of the invention, material isremoved from a balloon that has already been formed.

Although any of the above materials removal techniques may be employed,it is desirable when grinding subsequent to stretching to hold thetemperature of the preform below the glass transition temperature asdescribed above. This technique may be particularly useful in theformation of Pebax®, PBT and PET balloons.

The invention is also directed to a medical balloon having a proximalwaist portion, a proximal cone portion, a body portion, a distal coneportion and a distal waist portion wherein at least one of the proximalcone and waist wall thicknesses and distal cone and waist wallthicknesses is less than the body wall thickness, at least one of theproximal waist and cone portions and distal waist and cone portionshaving had material removed therefrom.

Where the wall thickness of the given portion is not constant, as withmany balloons, desirably, the average wall thickness of at least one ofthe proximal cone and waist portions and distal cone and waist portionsis less than the body wall thickness.

The invention is also directed to a medical balloon having a distal conewhose wall thickness is less than the wall thickness of the proximalcone. Where the wall thickness of the distal and proximal cones varies,desirably, the average wall thickness of the distal cone will be lessthan the average wall thickness of the proximal cone.

The invention is also directed to a medical balloon which when inflatedto a desired pressure has a constant wall thickness over substantiallythe entire portion of the balloon including the cone and body portions.Such a balloon may be prepared by removing a sufficient amount ofmaterial from the proximal and/or distal waist and/or cone portions ofthe balloon.

The invention is illustrated by the following non-limiting examples. Ineach of the following examples, the distal and proximal ends of a tubewere ground using a centerless grinder at room temperature. The tube wascooled using a water spray. Following grinding, the tube was stretchedat room temperature until a visual change in the outer diameter of thetube was noticed. The tube was then oriented with the ground section inthe cone region of a mold and lowered, ground portion first, into a 95°C. water bath. The tube was immersed to approximately the transitionlevel between the ground and non-ground section. The first groundsection was blown at a pressure of from about 350 to about 450 poundsper square inch (psi) to form the first cone and the mold was thenimmersed further into the water bath and the body section blown at apressure of from about 300 to about 350 psi. Finally, the second groundportion was immersed in the bath and blown to form a second cone at apressure of from about 350 to about 450 psi.

The following abbreviations and measurement units are used in the tablesbelow:

-   ID—inner diameter (reported in inches)-   OD—outer diameter (reported in inches)-   1×Wall—total wall thickness (reported in inches) including inner    wall and outer wall in the case of extruded tubing-   Outer Wall—thickness of outer layer of extruded tubing (reported in    inches)-   Inner Wall—thickness of inner layer of extruded tubing (reported in    inches)-   Grind OD—Outer diameter of tube in ground region (reported in    inches)-   New Wall—Wall thickness in ground region as given by Grind (OD−ID)/2    (reported in inches)-   % Grind—measure of percentage of material removed-   Taper length—length of transition between ground and unground    portions (reported in inches)

EXAMPLE 1

Coextruded tubing (inner layer Pebax 7233, outer layer Pebax 4033) wasground in accordance with the present invention and formed into aballoon using the method described immediately above. Measurements weremade for balloons formed from tubes with a grind transition 121 half wayalong the distal cone 115 (lower cone transition) shown schematically inFIG. 5 a and tubes with a grind transition 121 at the distal cone 115body 114 interface (upper cone transition) shown schematically in FIG. 5b. The wall thickness of the balloon was measured in the waist 116, halfway along the cone and in the body portion 114 of the balloon. For thesake of comparison, measurements were made on a balloon formed from anunground tube as well (non-grind). The measurements were repeated onballoons formed from four separate tubes. Reported below in Table 1 arethe measured single wall thicknesses in inches for samples 1-4. Theproperties of the initial tubes prior to blowing are reported in Table2. TABLE 1 Coex Sample × 10⁻³ in ×10⁻³ in Sample Distal 1 2 3 4 Avg.Nongrind Waist 6.50 6.25 6.55 6.30 6.40 ½ cone 1.95 2.00 2.10 2.40 2.11body 1.30 1.50 1.50 1.30 1.40 Lower cone trans. Waist 3.35 3.10 3.303.10 3.21 ½ cone 1.55 1.75 1.60 1.75 1.66 body 1.40 1.55 1.40 1.50 1.46Upper cone trans. Waist 3.20 3.35 3.25 3.30 3.28 ½ cone 1.50 1.35 1.501.50 1.46 body 1.40 1.50 1.55 1.55 1.50

TABLE 2 ID OD 1xWall Outer Wall Inner Wall Grind OD New wall % GrindTaper Length 0.0185 0.0453 0.0134 0.0054 0.0080 0.0383 0.0099 26% .0136

The balloons of example 1 had a cone length of 2.5 mm and a cone angleof 45°.

EXAMPLE 2

Polybutyleneteraphthalate (PBT) tubing was ground in accordance with thepresent invention and formed into a balloon using the method describedabove. The wall thickness of the balloon was measured in the waist, onethird of the way along the cone, two thirds of the way along the coneand in the body portion of the balloon. As shown schematically in FIGS.6 a and 6 b, measurements were made for balloons formed from tubes witha grind transition 121 two thirds of the way along the distal cone 115and tubes with a grind transition 121 at the distal cone 115-body 114interface (upper cone transition). For the sake of comparison,measurements were made on a balloon formed from an unground tube as well(non-grind). The measurements were repeated on four separate tubes.Reported below in Table 3a are the measured single wall thicknesses ininches.

Measurements were also made on PBT balloons with proximal cones groundas described above and reported below in Table 3b.

The properties of the initial tubes are reported in Table 4. TABLE 3aPBT Sample × 10⁻³ in ×10⁻³ in Distal 1 2 3 4 Avg Control Waist 2.80 2.902.90 2.85 2.86 ⅓ cone 1.55 1.30 1.50 1.50 1.46 ⅔ cone 1.05 0.95 0.950.95 0.98 body 0.75 0.65 0.75 0.70 0.71 Cone Trans. Waist 1.70 1.75 1.851.85 1.79 ⅓ cone 0.90 0.95 1.00 1.00 0.96 ⅔ cone 0.70 0.65 1.00 0.950.83 body 0.75 0.65 0.70 0.75 0.71 Body Trans. Waist 1.95 1.80 1.95 1.851.89 ⅓ cone 0.95 0.95 1.00 0.80 0.93 ⅔ cone 0.65 0.50 0.50 0.40 0.51body unground 0.75 0.65 0.70 0.75 0.71 body ground 0.35 0.40 0.40 0.300.36

TABLE 3b PBT Sample × 10⁻³ in ×10⁻³ in Proximal 1 2 3 4 Avg NongrindWaist 2.25 2.25 2.0 2.40 2.30 ⅓ cone 1.50 1.65 1.5 1.60 1.58 ⅔ cone 1.001.15 0.5 0.85 0.99 body 0.70 0.75 0.70 0.70 0.71 Cone Trans. Waist 1.401.65 1.25 1.45 1.44 ⅓ cone 1.50 1.70 1.50 1.30 1.50 ⅔ cone 0.90 1.101.00 1.00 1.00 body 0.70 0.75 0.70 0.65 0.70

TABLE 4 Taper ID OD 1xWall Grind OD New Wall % Grind Length 0.01500.0380 0.0115 0.032 0.0085 26% 0.03

The balloons of example 2 had a cone length of 4.0 mm and a cone angleof 15°.

EXAMPLE 3

Pebax 7233 tubing was ground in accordance with the present inventionand formed into a balloon using the method described above. The wallthickness of the balloon was measured in the waist, one third of the wayalong the cone, two thirds of the way along the cone and in the bodyportion of the balloon. Measurement were made for balloons formed fromtubes with a 30% wall grind and a 40% wall grind. As shown schematicallyin FIG. 7, the grind transition 121 was ⅔ of the way along the distalcone 115. For the sake of comparison, measurements were made on aballoon formed from an unground tube as well (non-grind). Themeasurements were repeated on four separate tubes. Reported below inTable 5 are the measured single wall thicknesses in inches.

The properties of the initial tubes are reported in Table 6. TABLE 5Distal Quantum Sample × 10⁻³ in ×10⁻³ in Nongrind 1 2 3 4 Avg. Waist3.70 3.85 3.70 3.45 3.68 ⅓ cone 2.10 2.40 2.50 2.45 2.36 ⅔ cone 1.001.35 1.25 1.30 1.23 body 0.75 0.85 0.85 0.75 0.80 24% wall Waist 3.103.15 2.80 3.05 3.03 ⅓ cone 1.25 1.60 1.20 1.20 1.31 ⅔ cone 1.00 1.101.05 1.00 1.04 body 0.85 0.85 0.85 0.90 0.86 34% wall ground Waist 2.102.10 1.80 2.20 2.05 ⅓ cone 0.55 0.60 0.55 0.65 0.59 ⅔ cone 0.90 0.950.11 0.90 0.96 body 0.85 0.85 0.85 0.90 0.86

TABLE 6 New ID OD 1xWall Grind OD Wall % Grind Taper Length 0.019 0.0360.0085 0.0309 0.0060 30% 0.03 0.019 0.036 0.0085 0.0292 0.0051 40% 0.03

The balloons of example 1 had a cone length of 4.0 mm and a cone angleof 15°.

EXAMPLE 4

Pebax 7233 tubing was ground in accordance with the present inventionand formed into a balloon using the method described above. The wallthickness of the balloon was measured in the waist, one third of the wayalong the cone, two thirds of the way along the cone and in the bodyportion of the balloon. Measurements were made for balloons formed fromtubes with a 24% wall grind and a 35% wall grind. Tubes were ground witha 32 mm backoff and a 33 mm backoff. As shown in FIG. 8, the 31 mmbackoff line is indicated by reference numeral 123, the 32 mm backoffline is indicated by reference numeral 124 and 33 mm backoff line isindicated by reference numeral 125. For the sake of comparison,measurements were made on a balloon formed from an unground tube as well(non-grind). The measurements were repeated on four separate tubes.Reported below in Tables 7a-d are the measured single wall thicknessesin inches for balloons formed from tubes with a 30% distal grind and 30%proximal grind and for balloons formed from tubes with a 40% distalgrind and 20% proximal grind.

The properties of the initial tubes are reported in Table 8. TABLE 7aGrind Distal 30% Proximal 30% 5.0 Leap II Sample × 10⁻³ in ×10⁻³ inDistal Portion 1 2 3 4 Avg Nongrind 0 5.25 5.85 5.35 5.35 5.45 1 2.901.80 2.80 1.90 2.35 2 1.95 1.30 1.85 1.55 1.66 3 1.40 1.10 1.35 1.201.26 4 1.10 1.00 1.10 1.10 1.08 5 0.85 0.80 0.95 1.00 0.90 32 mm backoff0 3.80 3.75 3.50 3.55 3.65 1 1.80 1.90 1.75 1.85 1.83 2 1.20 1.40 1.051.60 1.31 3 0.90 1.00 0.90 0.85 0.91 4 1.05 1.05 1.10 1.00 1.05 5 0.951.05 0.95 0.95 0.98 33 mm backoff 0 3.60 3.60 3.75 3.70 3.65 1 2.10 1.951.90 1.85 1.95 2 0.75 1.00 1.00 0.95 0.90 3 0.95 0.75 0.80 0.85 0.84 40.90 0.90 0.85 0.90 0.89 5 1.00 1.00 1.00 1.05 1.01

TABLE 7b Grind Distal 30% Proximal 30% 5.0 Leap II Sample × 10⁻³ in×10⁻³ in Proximal Portion 1 2 3 4 Avg Nongrind 0 5.35 5.00 4.75 4.754.96 1 2.95 3.25 2.70 3.00 2.98 2 2.05 1.80 1.75 1.95 1.89 3 1.30 1.301.25 1.25 1.28 4 1.10 1.15 1.00 1.10 1.09 5 1.05 1.00 1.00 1.00 1.01 32mm backoff 0 2.30 2.75 2.75 2.70 2.63 1 1.45 1.95 1.65 1.80 1.71 2 1.051.30 1.05 1.20 1.15 3 0.80 0.95 0.85 0.85 0.86 4 0.70 0.75 0.70 0.600.69 5 1.00 1.05 1.00 1.00 1.01 33 mm backoff 0 2.90 2.45 2.60 2.70 2.661 2.05 1.45 1.65 2.00 1.79 2 1.50 1.05 1.15 1.25 1.24 3 1.00 0.75 0.900.85 0.88 4 0.75 0.65 0.65 0.70 0.69 5 1.10 1.00 1.05 0.75 0.98

TABLE 7c Grind Distal 40% Proximal 20% 5.0 Leap II Sample × 10⁻³ in×10⁻³ in Distal 1 2 3 4 Avg Nongrind 0 5.25 5.85 5.35 5.35 5.45 1 2.901.80 2.80 1.90 2.35 2 1.95 1.30 1.85 1.55 1.66 3 1.40 1.10 1.35 1.201.26 4 1.10 1.00 1.10 1.10 1.08 5 0.85 0.80 0.95 1.00 0.90 31 mm backoff0 2.30 2.40 2.30 2.40 2.35 1 1.05 1.45 1.00 1.25 1.19 2 1.15 1.35 1.201.20 1.23 3 1.15 1.20 1.10 1.20 1.16 4 1.05 1.10 1.05 1.05 1.06 5 0.951.00 0.95 1.00 0.98 32 mm backoff 0 2.40 2.45 2.50 2.40 2.44 1 1.30 1.301.30 1.00 1.23 2 0.85 0.80 1.00 0.85 0.88 3 0.95 0.95 1.10 1.00 1.00 41.00 1.00 1.05 0.95 1.00 5 1.00 1.00 0.95 0.95 0.98

TABLE 7d Grind Distal 40% Proximal 20% Leap II Sample × 10⁻³ in ×10⁻³ inProximal Portion 1 2 3 4 Avg Nongrind 0 5.35 5.00 4.75 4.75 4.96 1 2.953.25 2.70 3.00 2.98 2 2.05 1.80 1.75 1.95 1.89 3 1.30 1.30 1.25 1.251.28 4 1.10 1.15 1.00 1.10 1.09 5 1.05 1.00 1.00 1.00 1.01 31 mm backoff0 3.60 3.70 3.70 3.70 3.68 1 2.10 2.40 2.20 2.25 2.24 2 1.40 1.45 1.301.40 1.39 3 1.00 1.00 1.05 1.00 1.01 4 0.95 0.90 1.00 1.00 0.96 5 1.051.00 1.05 1.05 1.04 32 mm backoff 0 3.40 3.65 3.70 3.60 3.59 1 2.05 2.402.45 1.90 2.20 2 1.40 1.50 1.45 1.20 1.39 3 1.05 1.15 1.10 1.00 1.08 41.05 1.10 1.05 1.10 1.08 5 1.10 1.05 1.05 1.00 1.05

TABLE 8 % ID OD 1xWall Grind OD New Wall Grind Taper Length Distal0.0334 0.055 0.0108 0.0499 0.0083 24% 0.04 0.0334 0.055 0.0108 0.04740.0070 35% 0.04 Proximal 0.0334 0.055 0.0108 0.0518 0.0092 15% 0.03

The balloons of example 1 had a cone length of 7.5 mm and a cone angleof 15°.

EXAMPLE 5

A balloon made of tubing subject to a 30% grind at the distal end, aballoon made of tubing subject to a 30% grind at both the distal andproximal ends, a balloon made of tubing subject to a 40% grind at thedistal end and a control balloon made of non-ground tubing weresubjected to a tensile test. The force required to pull a balloon conethrough a predetermined orifice size at a constant rate of travel wasmeasured for each of the balloons. The balloons were pulled at a rate of5 inches per second with a one hundred pound load cell. The orificediameter was 0.042 inches and the ratio of the distal outer diameter tothe orifice diameter was 0.70. The gauge length was 10 mm.

As shown in FIG. 9, the peak force required to pull the control balloonthrough the orifice as its distal cone enters the orifice is far inexcess of the peak force required for the inventive balloons. Reductionsin force can exceed 50%. Similarly, as the proximal cones pass throughthe orifice, the balloon which has been ground in the proximal coneregion requires a significantly lower load (in excess of 50%) to passthrough the orifice.

The instant example demonstrates that balloons formed in accordance withthe instant invention may exhibit reduced cone and waist stiffness.Other benefits that may result from the inventive balloons includebetter balloon folding capability, lower balloon profile, greater tipflexibility and improved retraction performance of retaining sleeveswhich are often placed about the cones of a balloon.

In addition to being directed to the embodiments described above andclaimed below, the present invention is further directed to embodimentshaving different combinations of the features described above andclaimed below. As such, the invention is also directed to otherembodiments having any other possible combination of the dependentfeatures claimed below.

The above examples and disclosure are intended to be illustrative andnot exhaustive. These examples and description will suggest manyvariations and alternatives to one of ordinary skill in this art. Allthese alternatives and variations are intended to be included within thescope of the attached claims. Those familiar with the art may recognizeother equivalents to the specific embodiments described herein whichequivalents are also intended to be encompassed by the claims attachedhereto.

1-32. (canceled)
 33. A method comprising the steps of: providing asegment of thermoplastic material tubing having a predetermined wallthickness and length, the segment having a proximal end portion, adistal end portion and a center portion; removing material from an outersurface of at least one of the distal and proximal end portions of thesegment to a desired reduced thickness while maintaining the temperatureof substantially all of the segment below about the glass transitiontemperature of the thermoplastic material.
 34. The method of claim 33,wherein the segment comprises a block copolymer, and during the removingstep, the temperature of substantially all of the segment is maintainedbelow the highest glass transition temperature of the block copolymer.35. The method of claim 33, wherein the material is removed by chemicaletching.
 36. The method of claim 35, wherein chemical etching comprisesselective masking of the segment.
 37. The method of claim 33, whereinthe material is removed by grinding.
 38. The method of claim 37, whereinthe material is removed using a centerless grinder.
 39. The method ofclaim 37, wherein the material is removed by disposing the segmentbetween a grinding wheel and a regulating wheel.
 40. The method of claim33, wherein after the removing step, the thickness of the proximal endportion and the thickness of the distal end portion differ.
 41. Themethod of claim 33, wherein after the removing step, the wall thicknessof the center portion is greater than the wall thickness of the at leastone end portion from which material is removed.
 42. The method of claim33, wherein material is removed from both the proximal end portion andthe distal end portion of the segment during the removing step.
 43. Themethod of claim 42, wherein more material is removed from the distal endportion than from the proximal end portion.
 44. The method of claim 33,further comprising the step of: drawing the segment to a predeterminedlength.
 45. The method of claim 44, wherein during the drawing step thetemperature of the segment is maintained below the glass transitiontemperature of the thermoplastic material or below the highest glasstransition temperature of the thermoplastic material if the material isa block copolymer.
 46. The method of claim 44, wherein after the drawingstep the wall thickness of the center portion is greater than the wallthickness of the proximal and distal end portions.
 47. The method ofclaim 33, wherein during the removing step the entire segment ismaintained below the glass transition temperature of the thermoplasticmaterial or below the highest glass transition temperature of thethermoplastic material if the material is a block copolymer.
 48. Themethod of claim 33, wherein a coolant is directed at the segment duringthe removing step to cool the segment.
 49. The method of claim 48,wherein the portion from which material is removed is maintained at atemperature cooler than the remainder of the segment.
 50. A preform fora medical balloon made in accordance with the method of claim
 33. 51.The method of claim 33, further comprising the step of: expanding thesegment in a mold to produce a medical balloon.
 52. A medical balloonmade in accordance with the method of claim 51.